Functional Evolution of Locomotor Posture in Tetrapods

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The early terrestrial vertebrates are thought to have had a sprawling posture, as do modern salamanders, where the limbs are held laterally to the body. Erect posture, where the limbs are held directly under the body, is thought to have evolved twice, once in the ancestors of mammals and once in the lineage containing dinosaurs (archosaurs). The biomechanical consequences of these different postures have been little studied and the hypothesis of a three-grade postural system (sprawling, semi-erect, and erect postures) has been recently questioned. A quantitative understanding of locomotor posture in living tetrapods with different postures is necessary to evaluate the consequences of this postural shift in the evolution of terrestrial tetrapods. The general goal of this study is to complete functional morphological analyses of hind limb kinematics and whole body kinetics (ground reaction forces and external mechanical work) during locomotion in a series of extant taxa representative of each major tetrapod class. These data will then be used to define, compare, and contrast various tetrapod postures in order to test a series of hypotheses about postural function and evolution in vertebrates. They will also be used to determine whether and how force dynamics of the limbs have changed during the evolutionary shift from sprawling to erect postures.